The most likely cause of the mysterious noise in the cemetery is an animal. Animals, especially nocturnal ones, can create unexpected sounds in outdoor environments, particularly at night when they are more active. While the idea of a spirit or the caretaker making noise is possible, animals are a more common and logical explanation for such sounds. Spirits have not been proven to exist, and the caretaker would typically have a reason for being in the cemetery. Although another boy could also be a possibility, animals are frequently found in outdoor areas like cemeteries, making them the most plausible source of the noise.